Grandisol (10) is stereoselectively synthesized in 9 steps, starting from commercially available 3-methyl-3-buten-1-ol (1). The key step of the synthesis is the Cu(I)-catalyzed [2 + 2]-photocycloaddition of 3 to 4a or 4b. Moreover, solvent effects on the endo/exo product ratio of the [2 + 2]-photocycloaddition are investigated.